This invention relates to an improved method of manufacturing capacitors, particularly to multiple layer ceramic-type capacitors.
A multiple-layer-ceramic-type capacitor comprises alternating thin layers of body electrode members, usually formed of silver palladium, and dielectric members. Alternate body electrodes typically, are connected to each other at one perimeter of the capacitor to form a positive terminal. The other body electrodes are connected to each other by a small quantity of termination compound at a different perimeter to form a negative terminal. Normally, the termination compound will contain a glass frit or another compound to improve its bonding ability to the capacitor. Most of the termination compound will comprise an electrically conductive metal mass, often a silver-bearing solder, that will readily fuse into an electrical circuit structure when heated to, typically, a 500.degree.-700.degree. C. terminating temperature.
A problem in manufacture of such capacitors has been the tendency of silver to be leached from the electrode into the body of the termination material during the termination process, thus causing infusion or no connections to some electrodes. The problem is one which is not readily controlled and varies in effect depending on the precise processing conditions and the precise nature of the materials being used. Nevertheless, such leaching is a substantial problem in capacitor manufacture of the type using body electrodes comprising a major portion of silver.
The present inventor has directed his attention to the mitigation of the problem. In so doing, he has discovered a primary improvement in the capacitor-terminating art and, also a number of secondary advantages that tend to improve the terminating art still further.
Cited below are some references which were found in a novelty search directed to the present invention. The search necessarily was carried out after the invention was made and with the invention in mind. Citation of these references is no admission that one skilled in the art, faced with the problem to which Applicant directed his attention, would have turned to these references at the time an invention was made.
Lasers have often been used to achieve special advantages in manufacture of electronic components. For example, U.S. Pat. No. 4,442,136 discloses a method for transient annealing of a phosphor coating in formation of AC-driven, thin-film, electroluminescent displays.
The following references describe the use of lasers in the formation of electrical components or circuits: U.S. Pat. No. 3,520,055 to Jannett; U.S. Pat. No. 4,238,661; U.S. Pat. No. 4,229,865. These patents describe cutting (trimming); connecting finished components together; and laser scribing onto the primary surface of a capacitor--another type of trimming operation. U.S. Pat. No. 4,327,277 describes the use of a laser in connecting an already-manufactured, multi-layer-ceramic capacitor, i.e. a capacitor already terminated (with apparently pre-existing "termination bands") and already containing a part-terminating solder layer for connection to a circuit. Similarly, in U.S. Pat. No. 4,439,814, Rhodes describes delayed trimming of a finished, circuit-mounted capacitor. In contrast to the above, the process described herein will relate to the field of manufacturing capacitors and to the avoidance of certain physical-chemical problems related precisely to the capacitor manufacturing step whereby a termination is attached to the capacitor chip.